Flat power-distribution cable

ABSTRACT

A flat cable for distributing electrical power between hingeable or demountable pieces of electrical apparatus is made up of thin, flat conductors nonrigidly mounted one on top of the other. The nonrigid mounting of the conductors relative to each other permits one to slip or slide relative to the other and thereby improve flexure of the cable and also increase the number of flexures the cable can be cycled through before it fails. Nonrigid mounting can be achieved by several different configurations. First, each flat conductor can be provided with its separate insulating layer and then the two insulated conductors may be held one over the other loosely so that they may slide or slip relative to each other. Second, a flat insulating cable may have a partition across its width so that one flat conductor may be placed in one partitioned section and the other flat conductor may be placed under the other conductor in the second partitioned section. Third, separately insulated conductors may be taped together at spaced locations so as to allow each conductor to slide within its own insulation and to allow relative movement of the conductors between the spaced locations.

UnitedStates Patent [72] Inventor Donald F. Colglazier Rochester, Minn.[21] AppLNo. 847,937 [22] Filed Aug. 6,1969 [45] Patented May 4,1971[73] Assignee International Business Machines Corporation Armonk,N.Y.Continuation-impart of application Ser. No. 696,595, Jan. 9, 1968, nowabandoned.

[54] FLAT POWER-DISTRIBUTION CABLE 15 Claims, 6 Drawing Figs.

[52] U.S.Cl 174/117, 174/113 [51] 1nt.Cl H01b7/08 [50] FieldofSearch174/113, l17,l17.l1,1l7.1,112(1nquired) [56] References Cited UNITEDSTATES PATENTS 3,459,880 8/1969 Erdle 174/117 286,829 10/1883Kohmescher... 174/113UX 2,805,472 9/1957 Botts l74/113X 2,361,37410/1944 Abbott.... 174/117UX 3,239,916 3/1966 Love ..174/ll7(.11)X3,304,364 2/1967 Hetherington. 174/117X 3,345,455 10/1967 Goody 174/1128/1968 Crimmins ..l74/l17(.ll)X 8/1969 Gerpheide 174/1l7(.ll)

FORElGN PATENTS 712,656 12/1964 Canada ABSTRACT: A flat cable fordistributing electrical power between hingeable or demountable pieces ofelectrical apparatus is made up of thin, flat conductors nonrigidlymounted one on top of the other. The nonrigid mounting of the conductorsrelative to each other permits one to slip or slide relative to theother and thereby improve flexure of the cable and also increase thenumber of flexures the cable can be cycled through before it fails.Nonrigid mounting can be achieved by several different configurations.First, each flat conductor can be provided with its separate insulatinglayer and then the two insulated conductors may be held one over theother loosely so that they may slide or slip relative to each other.Second, a flat insulating cable may have a partition across its width sothat one flat conductor may be placed in one partitioned section and theother flat conductor may be placed under the other conductor in thesecond partitioned section. Third, separately insulated conductors maybe taped together at spaced locations so as to allow each conductor toslide within its own insulation and to allow relative movement of theconductors between the spaced locations.

PATENTED m 4m SHEET 1 0F 2 FIG.I

INVENTOR. DONALD F. COLGLAZlER ncrzm CROSS-REFERENCE TO RELATEDAPPLICATIONS The present application is a continuation-in-part ofcopending and now abandoned Ser. No. 695,595, filed Jan. 9, I968 byDonald F. Colglazier and assigned to the assignee of the presentapplication.

Background of the Invention This invention relates to power cables andmore particularly to flat cables as commonly used in distributing powerto electronic systems.

The broad concept of a flat power cable is quite old; however to date,all of these flat power cables have been susceptible to damage when theywere bent sharply. Bending of these cables would cause conductors topull through the insulation and short out to each other or to achassisaround which the cables were bent. Also if the cable successfullysurvived one flexure, reflexing the cable to a new position would causethe cable to fail by shorting out or by metal fatigue.

Some of the prior art cable designs are simply two flat conductorsmounted rigidly in the same insulating medium. Another flat cable designis where multiple conductors are placed in the same flat cable by havinga flat conductor at the bottom of the cable and multiple wire conductorsplaced immediately over the flat conductor with all of these conductorsbeing bonded to the same insulating material to make up the cable. Ineither of these two types of cables if a sharp flexure occurs, the metalconductor on the outside of the flexure will have to stretch more thanthe other inner conductor to make the bend. This additional stretch putsadditional tension in the outer conductor tending to pull it throughinsulation towards the inner conductor.

If the prior art cables happen to survive the initial flexure withoutshorting, their insulating material will usually be so damaged that tostraighten the cable and form another flexure will almost certainlycause the cables to either short to the chassis around which they arebeing bent or to short one to the other.

The problem is how to prevent a conductor in a flat cable from beingpulled through the insulation to another conductor in a flat 'cable whenthe cable is bent or flexed sharply around a comer.

Cables in accordance with the invention find primary applications inconnection with electrical apparatus constructed from a number ofswingable, hingeable or demountablc sections, wherein various supply andbias voltages must be routed to some or all sections at high currentlevels. More specifcally, most large-scale computers and similar deviceshave a stationary main frame containing central power supplies, and anumber of "gates hinged therefrom so as to swing outwardly for servicingand inspection. Each gate, commonly 3 feet square or larger, containsmany thousands of individual circuits mounted on cards or boardsattached to the gate. It is therefore not unusual for even a single gateto require supply currents on the order of 30 to I amperes or more. Atthe same time such cables must be capable of sustaining repeatedflexures over bending diameters as small as one to four inches. Priorattempts to meet these twin requirements have employed large, roundstranded wires, parallel smaller stranded wires arranged in a flatconfiguration, and single flat conductors of the relatively thick busbar variety. None of these attempts, however, has provided an adequatesolution, and the lack of such a solution is today a major impediment tothe fabrication of easily serviceable large-scale computers and otherequipment.

It is therefore an object of this invention to produce a new flat cablewhich has great flexibility and can be cycled through multiple flexureswithout destroying its electrical integrity.

It is a further object of the invention to produce a flat power cablewhich may be flexed around sharp corners and wherein the outer conductorof the bend will not be pulled through the insulation to short againstthe inner conductor of the bend.

2 SUMMARY or rnrz INVENTION In accordance with the invention the aboveobjects are accomplished by nonrigidly mounting the conductors in theflat cable so that the conductors are free to slide or slip relative toeach other. In one embodiment of the invention,.two flat conductorsareinsulated separately with their own slidable insulating layers andthe resulting insulated conductors and then placed in a loose casingwith one insulated conductor laying on top of the other insulatedconductor. The insulated conductors are held loosely in position overeach other by an outer casing. Each insulated conductor can sliderelative to the other conductor and can also slide relative to the outercasing. ln an alternative embodiment, the separately insulatedconductors are fastened together by spaced tapes or bands which, whilepreventing substantial relative movement between the insulators at thetaped locations, still permit each conductor to slide within its owninsulator, and further permit the conductors to move toward or away fromeach other between the taped locations. In a further embodiment, theindividual flat conductors do not have a layer of insulation bondedaround them but instead are mounted in an insulated cable or casingwhich is partitioned. The partition lies horizontally across the widthof the cable so that the partition separates the two flat conductors.Each conductor is held loosely in its partitioned section of the casingso that the conductors can slide along the length of the casing relativeto each other and to the casing.

The great advantage of the invention is that it is very flexible andeven after many flexures the conductors will not pull through theinsulation or fail in fatigue. The conductors do not pull through theinsulation because they are slidable mounted in the cable, and thereforethe stretch or stress built up in a conductor when the cable is bentaround a corner is evenly distributed along the length of the conductorsince the entire conductor can stretch to make the bend.

Stated another way, in the prior art where conductors were rigidly tiedto insulating material and to each other, the stresses built up upon aconductor at a corner were restricted to a small length of theconductor. Great force built up tending to pull the conductor throughthe insulation. In the subject invention because the conductor isslidably mounted relative to the other conductor the stress is evenlydistributed over a great length of conductor; therefore, forces causingthe conductor to be pulled through the insulation are greatly reduced.

The provision of interior slip planes between each individual conductorand its associated insulative covering is especially to be noted. Thatis, each individual conductor may move relative to its immediatelyadjacent insulating layers, even if the insulation of one conductor isrigidly mounted to the insulation of another conductor. This aspect ofthe invention not only leads to ease the manufacture of such cables, butalso enhances its stress-relieving properties, since the stress isrelieved at many more points, and since the stress on the insulatinglayers is not permitted to add to the stress on their associatedconductors in any significant manner. This method of stress relief hasbeen completely unappreciated by the priorart flat cables of whichapplicant is aware.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a flat power cableimplemented by separately insulating each flat conductor.

FIG. 2 shows a flat power cable implemented by placing two flatconductors in separate partitions of an insulated casing.

FIGS. 3a and 31: show multiple conductor embodiments of the inventionutilizing conductors which are each insulated as in FIG. 1.

FIG. 4 illustrates, in a flexed condition, a multiple-conductor cableemploying tapes at spaced locations.

FIG. 5 is a perspective view, partly in cross section, of an individualconductor assembly for. use with the embodiments of FIGS. 1, 3a, 3b and4.

DESCRIPTION Referring now to FIG. 1, two flat conductors 10 and 12 aresurrounded by insulating material. Flat conductor 10 has bonded to it alower insulating layer 14 and upper insulating layer 16. A flatinsulated conductor can be formed by laying the flat conductor 10 on alayer of insulating material 14 and then overlaying the assembly withanother layer of insulating material 16 and heat bonding the assembly.Conductor 12 is similarly insulated by insulating layers 18 and 20. Theentire assembly of conductors l and 12 with their insulating layers iscontained in a flexible casing 22. The function of the casing is to keepone insulated conductor positioned over the other conductor. The casingcould be replaced by any mounting device which would keep the insulatedconductors properly positioned without rigidly holding them.

The significant fact of the construction of the cable and the essence ofthis embodiment of the invention is that the insulated conductorassembly 17 and the insulated conductor assembly 21 are not rigidlymounted to each other or to the easing 22. In particular, the casing 22has sufficient inner dimensions to allow for a slip plane 24 between theinsulated concluctor assemblies 17 and 21 and also for a slip plane 26above the assembly 21 and some space 28 below the assembly 17. As

a result, the conductive assemblies 17 and 21 are free to slide alongthe length of the cable relative to each other and relative to thecasing 22. As previously pointed out by having the conductors slidablymounted, the cable assembly may be flexed about sharp bends without theconductors pulling through the insulating and shorting out.

F IG. depicts, in greatly exaggerated size but approximately correctrelative proportions, a preferred form of conductor assembly 17 ofFIG. 1. Conductor assembly 21 (as well as corresponding assemblies shownin FIGS. 30 and 3b) is preferably of a similar construction.

The lengthwise or longitudinal conductor is shown in FIG. 5 as ametallic strip having a substantially rectangular cross section and awidth-to-thickness ratio, or aspect ratio, which is extremely high incomparison to previous flat conductors used for power-distributionpurposes. A broad optimum for low-voltage distribution systems, forinstance, has been found to lie in the neighborhood of a 1000 mil by 10mil cross section, i.e., an aspect ratio of 100:1. Minimum width isconstrained to be at least about 500 mils for adequate currenthandlingcapability; maximum width is limited, primarily by the space availablein associated electrical equipment, to about 3000 mils. Current-handlingcapability and mechanical strength dictate that the conductor thicknessbe above ap proximately 5 mils. Maximum thickness is fairly sharplylimited by metal fatigue and flexibility to about 30 mils. Morespecifically, it has been found that the present aluminum alloys areentirely unsatisfactory at a 50-mil thickness, which is a very smallthickness in the power-distribution arts. Even a -mil thicknessdimension has been found to have perceptibly inferior fatigue resistanceas compared to the lO-mil optimum, Therefore, it is preferable toincrease current ratings by employing parallel, individually insulatedconductors of IO-mil to 20-mil dimensions rather than by increasing thethickness much beyond 20 mils.

The above thicknesses are for commercially pure l 100 aluminum accordingto ASTM Standard B21l-68, which combines favorable electrical andstructural properties in relation to present-day cost and availability.Although other metals or alloys may become preferable in terms of theabove trade-offs, it is considered doubtful that thicknesses much morethan mils would be useful in the present invention. Within the abovelimits, the aspect ratio of the conductor should be greater than about25:1 to ensure that the conductor lies flat without twisting or turningsufficiently to rupture the insulative covering or to change theorientation of the cable conductors relative to each other. On themaximum side, the aspect ratio should be restricted to less thanapproximately 300:1 in order to prevent curling of the conductor in atransverse (width) direction within its insulative covering.

The insulative layers 14 and 16 are shown in FIG. 5 as thin, flat,pliable strips having edge regions 41 extending outwardly in atransverse direction beyond the edges 42 of conductive strip 10. Sincestrips 14 and 16 are wider than conductor 10, regions 41 of insulator 14will directly underlie corresponding regions 41 of insulator 16.Corresponding edge regions 41 may then be bonded to each other in one ofa number of simple, conventional and inexpensive manufacturingtechinques. If, for example, strips 14 and 16 are made of athermoplastic such as polyethylene or Mylar (a trademark of E. I. duPontde Nemours & Co. for a polyester film), a sandwich comprising strips 10,14 and 16 may be fed from continuous rolls past heated rollers (notshown) for edge-bonding. Strips 14 and 16 will adhere only to each otherand not to the conductive strip 10. The aforementioned high aspect ratioof conductor 10 and the pliability of strips 14 and 16 ,then combine toprovide an insulative casing which establishes slip planes 43 betweenthe surfaces of conductor 10 and the interior surfaces of strips 14 and16, so as to allow lengthwise or longitudinal relative movementtherebetween. The proximity of edge regions 41 to the conductor edges42, however, prevents any substantial transverse or lateral movement ofthe encased conductor. The apparently contradictory requirements oflengthwise mobility and transverse restriction disappear almost entirelyfor the high conductor aspect ratios noted hereinabove. FIG. 5 depicts,for example, the loose fit between conductor and insulators in thedirection perpendicular to both the longitudinal and transversedirections. This effect proceeds from the fact that the change in lengthof strip 14 or 16 to achieve a given vertical separation from conductor10 becomes considerably less for a high aspect ratio. In addition, thislarge width-tothickness ratio greatly decreases the angles betweenstrips 14 and 16 adjacent the bonded regions 41. Thus only a portion ofedges 42 actually bear against strips 14 and 16, and the relativestiffness of conductor 10 causes it to act as a wedge attempting toseparate the strips. Thus, the above configuration produces a pair oftriangular or wedge-shaped interior spaces 50 enclosed by the conductoredges 42 and the strips 14 and 16. Since the angles between strips 14and 16 are small, the angles between each strip and the edges 42 arerelatively large.

The edge-bonded regions 41 must, of course, be sufficiently wide tosecure an adequate bond and to prevent rupture thereof by the conductor.But again the high aspect ratio of the conductor proves to be anadvantage. With no tensile stress being imposed in the verticaldirection by the wide, flat surfaces of conductor 10, the bonds needwithstand only the slight wedging forces relative motion which is skewedfrom the lengthwise direction. Since the purpose of lengthwise relativemotion is only to relieve compressive and tensile stresses in theassembly 17, the actual amount of the motion is very small in relationto both the length and the width of the assembly, and the maximumpossible skew is therefore insignificant. For the l000-mil by lO-milconductor described above, e.g., the total width of each strip 14 and 16may be approximately 1 mils (i.e., l /ainches), yielding on edge bond of30 to 50 mils on each side. That is, the extra width required for thebonded edge regions increases the total width of assembly 17 by onlyabout 10 percent for a conductor aspect ratio of 100:]. The thickness ofeach insulative strip 14 and 16 may conveniently be approximately 5 milsin this instance, depending for the most part on the magnitude of thevoltages to be carried.

The assembly specifically detailed here was designed to carry 5 volts ata current of 60 amperes in free air, derated to 30 amperes when used ina cable such as that shown in FIG. 1. A slightly larger assembly, havinga l000-mil by 12-mil alu minum conductor and l-mil by 8.5-milpolyethylene insulating layers, was tested for failure (conductorbreakage or insulator rupture) by weighing one end and bending itrl90over mandrels having various sizes. For mandrel diameters of V4, h

' and 1% inches, the average numbers of complete bending cycIes'to-causefailure were 735, 2000 and 5800, respectively,

This assembly was designed for bending diameters in the approximaterange of l to 4 inches. Under conditions of actual usage, therefore, itis virtually indestructible.

, Referring now to FIG. 2 an alternative embodiment of the invention isshown. In this alternative embodiment the flat conductors l0 and 12 aremounted looselyin a conductive casing 30 which has an insulatingpartition 32 to separate the conductors l0 and I2. The conductors l0 and12 are loosely mounted in the casing 30 having ample space for each con-7 ductor 10 or l2to slide along the length of the cable in its as- 40 issurrounded by insulating layers or strips just as described inconnection with FIGS. I and 5. Each insulated conductor assembly is thusa separate entity which is slidable relative to the other insulatedconductive assemblies.

FIG. 4 is a side elevation of a further embodiment according to thepresent invention. This form of the cable 45 employs a number of flatconductor assemblies 44, each of which is constructed in accordance withthe preceding description of representative assembly 17. The assembliesappear in an edgeon aspect in order to illustrate another type ofstress-relieving relative motion attainable under the invention. Moreparticularly, the cable of FIG. 1 permits substantial relative motion ofconductors 10 and 12 in only one direction perpendicular to 1 theconductor width, namely, in the lengthwise or longitudinal direction ofthe conductors. Cable 45, on the other hand, additionally allowssubstantial relative movement in-a vertical .direction, i.e., in adirection perpendicular both to the length and to the width of itsconductors.

Cable 45 comprises a stack of any number of flat conductor assemblies 44laid one on top of another; for clarity of description, only four suchassemblies are shown. Assemblies 44 are restrained by discrete bands orbindings 46 encircling the assemblies in the direction transverse totheir length and disposed at spaced locations 47 therealong. Bands 46may conveniently be strips of insulating adhesive tape adhering to atleast the two outer assemblies 44 and fastened upon themselves. For thel000-mil by IO-mil conductor size referred to above, the tapes'may be,e.g., from about /&inch to one inch wide, and the spaced locations 47may be, e.g., from about 3 inches to about 12 inches apart. The onlymajor requirements are that the locations 47 be sufficiently closetogether to prevent substantial transverse (i.e., perpendicular to theplane of FIG. 4) relative motion between assemblies 44, and that thetapes 46 be wide enough to avoid their cutting into the cable 45 and toavoid the imposition of extremely sharp bends in the cable when it isflexed near the locations 47. In other respects, the width of tapes 46and the spacing of locations 47 are design choices to be determined fromthe contemplated cable size and application.

Bindings 46 may alternatively be made of nonadhesive or evennoninsulating material. Where it is desired to affix the cable 45 to amechanical support, e.g., the restraining function of bind gs 46 may beaccomplished by a clamp (not shown) or similar means. Even when thebindings 46 adhere to some or all of the assemblies 44, the slip planes43, described in connection with FIG. 5, still allow longitudinalrelative movement among the individual conductors of the assemblies.Such movement may occur both at the spaced locations 47 and at alllocations 48 therebetween. In addition, the assemblies 44 have anotherdegree of freedom at the locations 48, as shown by the arrows 49 in FIG.4. That is, the restraining means 46, being interrupted along the lengthof cable 45, permit the individual assemblies 44 and their respectivelyencased conductors to move relative to each other in a direction whichis perpendicular both to their length and to their width.

The cable embodiment shown in FIG. 4 has three salient advantages, formany applications, over the preceding variations having continuouscasings. First, the fabrication of the cable is rendered easier andcheaper, especially in that it may be built up in situ to exactspecifications, without wastage, from a continuous roll containing asingle conductor assembly 44. Second, the provision for relativemovement in the direction 49 allows a large number of assemblies 44 tobe stacked into a single cable without the introduction of undue stress.This is particularly true when the cable is disposed within itsassociated equipment (not shown) such that flexure will force the cableinto the S-shape illustrated, since this configuration places onlyinsignificant longitudinal stresses upon assemblies 44, so that there isno tendency for the bindings 46 to be sheared or pulled out of shape. Asstated earlier, it is generally preferable to increase the current ofcapacity of cables according to the invention by paralleling conductorassemblies rather than by making the individual assemblies larger insize. Therefore this second advantage increases the current capabilityof the cable.

In the third place, the interrupted restraining means, and its attendantincrease in the number of assemblies in a single cable, allows lateralconnections or taps to the cable to be made in a simple manner. In manypowerdistribution systems, it is necessary that connections toindividual conductors of a cable or bus bar be brought out from theside. Conventional practice achieves this end by the use of tabs, asillustrated, e.g., by US Pat. No. l,999,l37. Such tabs, however, musteither be initially built into the conductors at specified locations orbe mechanically affixed thereto at installation. Either of thesealternatives increases the cost of the cable to a significant extent.Moreover, the only practical connections to the tabs are by means ofsubstantially round wires, which decrease flexibility, which tend tobreak the tabs by pulling and bending them, and which undesirablyincrease the inductance of the system. The cable 45 of FIG. 4 overcomesthese disadvantages by allowing a large number of stress-relievedparallel conductor assemblies such as 44. That is, cable 45 may containseveral assemblies 44 each carrying the same supply voltage. A' lateraltap may then be made at any location 48 merely by folding one entireassembly out of the cable, in any desired direction, and by connectingit directly to its individual load (not shown). Such folding is madepractical in the present invention, of course, by the very high aspectratio of the individual conductors, as pointed out hereinabove.

It will be appreciated by one skilled in the art that other electricalcable configurations can be designed using multiple flat conductors ofvarious configurations. Also in a two conductor cable the conductors canbe insulated from each other by giving only one conductor an insulatedcoating. An outer casing would position the conductors over each otherand insulate the uncoated conductor from conductive metal outside thecable.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

Iclaim: I. A cable for distributing electrical power, comprising: aplurality of conductor assemblies extending in a longitudinal direction,each said assembly including a thin flat conductive strip extending insaid longitudinal direction, a first pliable insulative stripimmediately and nonadheringly overlying said conductive strip and havinga plurality of edge regions extending outwardly beyond the edges of saidconductive strip in a direction transverse to said longitudinaldirection, and a second flat pliable insulative strip immediately andnonadheringly underlying said conductive strip and'having a pluralityofedge regions bonded only to corresponding ones of said firstnamed edgeregions so as to allow said conductive strip to move in saidlongitudinaldirection relative to each of said insulative strips; and restrainingmeans holding said conductor assemblies one on top of another so as toprevent substantial relative movement thereamong in said transversedirection while permitting relative movement thereamong in a directionperpendicular to said transverse direction. 2. A cable according toclaim 1 wherein said edge regions of said second insulative strip ofeach assembly extend outwardly beyond the edges of said conductive stripin said transverse direction, said conductor and said strips of eachassembly defining a pair of interior, substantially triangular spacesenclosed by the edges of said conductor and the bonded edge regions ofsaid strips, each said space-having one relative small acute angle andtworelatively large angles.

1 3. A cable according to claim 2 wherein said restraining meanscomprises a plurality of binding means disposed at spaced locationsalong said longitudinal direction for preventing, at said locations,substantial relative movement among said strips in a directionperpendicular to both said longitudinal and said transverse directions,and for permitting relative movement in said perpendicular direction atother than said locations upon flexure of said cable assembly.

'4. A cable according to claim 2 wherein the aspect ratio of each ofsaid conductors is greater than about 25:1.

5. A cable according to claim 4 wherein the thickness of each of saidconductors is less than approximately 30 mils.

6. A cable according to claim 5 wherein the thickness of each of saidconductors is less than or equal to approximately I 2 mils and the widthof at least one of said conductors is equal to or greater thanapproximately 1000 mils.

7. A flat cable for distributing electrical power, comprising: first andsecond lengthwise electrical conductors, each of said conductors beingof a substantially rectangular cross section and having a widthsubstantially exceeding a thickness thereof; insulating means having aplurality of pliable insulating layers immediately adjacent and slidablyencasing each of said conductors so as to permit lengthwise relativemotion between said conductors and said layers, each of said layershaving a width exceeding the width of said conductors associatedtherewith, at least two of said layers encasing each conductor beingedge-bonded to each other; and

. means supporting said first conductor on top of said second conductorso as to restrain relative movement therebetween in the direction ofsaid conductor width while permitting relative movement therebetween ina direction perpendicular to said conductor width.

' 8. A cable according to claim 7 wherein said conductors are slidablyencased by said insulating layers, said conductors and said layersdefining a plurality of substantially triangular spaces, each said spmehaving one relatively small acute angle and two relatively large angles.

9. A cableaccording to claim 8 wherein said insulating means comprises afirst pair of mutually edge-bonded insulating layers encasing said firstconductor and a second pair of mutually edge-bonded insulating layersencasing said second conductor.

10. A cable according to claim 9 wherein said supporting means encirclessaid conductors and both of said pairs of layers.

11. A cable according to claim 10 wherein said supporting meanscomprises a lengthwise pliable insulative sheath loosely means, each ofsaid binding means bonded to a plurality of said layers so as torestrict lengthwise relative movement between said layers and saidbinding means at the locations of said binding means, but so as topermit relative movement between said locations.

13. A cable according to claim 9 further comprising:

a third lengthwise electrical conductor, said third conductor being of asubstantially rectangular cross section and having a width substantiallyexceeding a thickness thereof;

a third pair of mutually edge-bonded insulative layers encasing saidthird conductor; and

wherein said supporting means is constructed and arranged for holdingsaid third conductor beside said first conductor so as to permitrelative movement between said second and said third conductors in adirection perpendicular to that of said conductor widths.

14. A cable according to claim 13 further comprising:

a fourth lengthwise electrical conductor, said fourth conductor being ofa substantially rectangular cross section and having a widthsubstantially exceeding a thickness thereof;

a fourth pair of mutually edge-bonded insulative layers encasing saidthird conductor; and

wherein said supporting means is constructed and arranged for holdingsaid fourth conductor beside said second conductor so as to permitrelative movement between said third and said fourth conductors in adirection perpendicular to said conductor widths.

15. A cable distributing electrical power, comprising:

a plurality of conductor assemblies extending in a longitudinaldirection, each said assembly including a thin flat conductive stripextending in said longitudinal direction, a first pliable insulativestrip immediately and nonadheringly overlying said conductive strip andhaving a plurality of edge regions extending outwardly beyond the edgesof said conductive strip in a direction transverse to said longitudinaldirection, and a second flat pliable insulative strip immediately andnonadheringly underlying said conductive strip and having a plurality ofedge regions extending outwardly beyond the edges of said conductivestrip in said transverse direction and bonded to corresponding ones ofsaid first-named edge regions so as to allow said conductive strip tomove in said longitudinal direction relative to each of said insulativestrips, said conductor and said strips of each assembly defining a pairof interior, substantially triangular spaces enclosed by the edges ofsaid conductor and the bonded edge regions of said strips, each saidspace having one relatively small acute angle and two relatively largeangles; and

restraining means comprising an insulative casing loosely disposed aboutsaid assemblies for holding said conductor assemblies one on top ofanother so as to permit relative movement thereamong in saidlongitudinal direction while preventing substantial relative movementthereamong in said transverse direction and in the directionperpendicular to both said longitudinal and said transverse directions.

1. A cable for distributing electrical power, comprising: a plurality ofconductor assemblies extending in a longitudinal direction, each saidassembly including a thin flat conductive strip extending in saidlongitudinal direction, a first pliable insulative strip immediately andnonadheringly overlying said conductive strip and having a plurality ofedge regions extending outwardly beyond the edges of said conductivestrip in a direction transverse to said longitudinal direction, and asecond flat pliable insulative strip immediately and nonadheringlyunderlying said conductive strip and having a plurality of edge regionsbonded only to corresponding ones of said first-named edge regions so asto allow said conductive strip to move in said longitudinal directionrelative to each of said insulative stripS; and restraining meansholding said conductor assemblies one on top of another so as to preventsubstantial relative movement thereamong in said transverse directionwhile permitting relative movement thereamong in a directionperpendicular to said transverse direction.
 2. A cable according toclaim 1 wherein said edge regions of said second insulative strip ofeach assembly extend outwardly beyond the edges of said conductive stripin said transverse direction, said conductor and said strips of eachassembly defining a pair of interior, substantially triangular spacesenclosed by the edges of said conductor and the bonded edge regions ofsaid strips, each said space having one relative small acute angle andtwo relatively large angles.
 3. A cable according to claim 2 whereinsaid restraining means comprises a plurality of binding means disposedat spaced locations along said longitudinal direction for preventing, atsaid locations, substantial relative movement among said strips in adirection perpendicular to both said longitudinal and said transversedirections, and for permitting relative movement in said perpendiculardirection at other than said locations upon flexure of said cableassembly.
 4. A cable according to claim 2 wherein the aspect ratio ofeach of said conductors is greater than about 25:1.
 5. A cable accordingto claim 4 wherein the thickness of each of said conductors is less thanapproximately 30 mils.
 6. A cable according to claim 5 wherein thethickness of each of said conductors is less than or equal toapproximately 12 mils and the width of at least one of said conductorsis equal to or greater than approximately 1000 mils.
 7. A flat cable fordistributing electrical power, comprising: first and second lengthwiseelectrical conductors, each of said conductors being of a substantiallyrectangular cross section and having a width substantially exceeding athickness thereof; insulating means having a plurality of pliableinsulating layers immediately adjacent and slidably encasing each ofsaid conductors so as to permit lengthwise relative motion between saidconductors and said layers, each of said layers having a width exceedingthe width of said conductors associated therewith, at least two of saidlayers encasing each conductor being edge-bonded to each other; andmeans supporting said first conductor on top of said second conductor soas to restrain relative movement therebetween in the direction of saidconductor width while permitting relative movement therebetween in adirection perpendicular to said conductor width.
 8. A cable according toclaim 7 wherein said conductors are slidably encased by said insulatinglayers, said conductors and said layers defining a plurality ofsubstantially triangular spaces, each said space having one relativelysmall acute angle and two relatively large angles.
 9. A cable accordingto claim 8 wherein said insulating means comprises a first pair ofmutually edge-bonded insulating layers encasing said first conductor anda second pair of mutually edge-bonded insulating layers encasing saidsecond conductor.
 10. A cable according to claim 9 wherein saidsupporting means encircles said conductors and both of said pairs oflayers.
 11. A cable according to claim 10 wherein said supporting meanscomprises a lengthwise pliable insulative sheath loosely encasing saidlayers and said conductors so as to permit lengthwise relative movementbetween said layers and said sheath.
 12. A cable according to claim 10wherein said supporting means comprises a plurality of spaced insulativebinding means, each of said binding means bonded to a plurality of saidlayers so as to restrict lengthwise relative movement between saidlayers and said binding means at the locations of said binding means,but so as to permit relative movement between said locations.
 13. Acable according to claim 9 further comprising: a third lengthwiseelEctrical conductor, said third conductor being of a substantiallyrectangular cross section and having a width substantially exceeding athickness thereof; a third pair of mutually edge-bonded insulativelayers encasing said third conductor; and wherein said supporting meansis constructed and arranged for holding said third conductor beside saidfirst conductor so as to permit relative movement between said secondand said third conductors in a direction perpendicular to that of saidconductor widths.
 14. A cable according to claim 13 further comprising:a fourth lengthwise electrical conductor, said fourth conductor being ofa substantially rectangular cross section and having a widthsubstantially exceeding a thickness thereof; a fourth pair of mutuallyedge-bonded insulative layers encasing said third conductor; and whereinsaid supporting means is constructed and arranged for holding saidfourth conductor beside said second conductor so as to permit relativemovement between said third and said fourth conductors in a directionperpendicular to said conductor widths.
 15. A cable distributingelectrical power, comprising: a plurality of conductor assembliesextending in a longitudinal direction, each said assembly including athin flat conductive strip extending in said longitudinal direction, afirst pliable insulative strip immediately and nonadheringly overlyingsaid conductive strip and having a plurality of edge regions extendingoutwardly beyond the edges of said conductive strip in a directiontransverse to said longitudinal direction, and a second flat pliableinsulative strip immediately and nonadheringly underlying saidconductive strip and having a plurality of edge regions extendingoutwardly beyond the edges of said conductive strip in said transversedirection and bonded to corresponding ones of said first-named edgeregions so as to allow said conductive strip to move in saidlongitudinal direction relative to each of said insulative strips, saidconductor and said strips of each assembly defining a pair of interior,substantially triangular spaces enclosed by the edges of said conductorand the bonded edge regions of said strips, each said space having onerelatively small acute angle and two relatively large angles; andrestraining means comprising an insulative casing loosely disposed aboutsaid assemblies for holding said conductor assemblies one on top ofanother so as to permit relative movement thereamong in saidlongitudinal direction while preventing substantial relative movementthereamong in said transverse direction and in the directionperpendicular to both said longitudinal and said transverse directions.